A few Chemistry questions...

[ada_t]

First of all, I would like to say hello and please excuse my English. I`ll do my best.

We (finally) did some experiments in our Chemistry class on Wednesday and my group was the first one to finish them all, so the teacher gave us some extra homework.

 

First experiment:

We had to use HCl, NaOH and phenolphthalein. We added HCl and 2-3 drops of phenolphthalein and then we added NaOH. When we added it, a white foam was formed and a gas was emitted. We poured more NaOH and the foam reappeared, but after a very short time it disappeared and the solution turned dark pink (or a combination of red and pink).

Why was that foam formed and why did the solution become dark pink? It usually used to have that color when phenolphthalein was added in NaOH or in any other solution containing "OH", so why is it different this time?

 

Second experiment:

We had to use CuSO4 and NaOH. We added 1-2 ml of CuSO4 and then 1 ml of NaOH. When we added NaOH a blue, insoluble precipitate was formed. As far as I know, the precipitate is Cu(OH)2, but my question is: why was it formed?

 

Thanks for reading!

Edited March 5, 2011 by ada_t

[ConejovampirO]

I'm not going to attempt to tell you that I am right, I will merely give advice on what I think.

 

Your reaction appears to be an acid/base titration. The phenolphthalein you added to the solution was an indicator. The indicator tells you when a difference in pH (acidic---> basic or vice versa, depending on your indicator) is achieved. The solution turned pink after you added NaOH to the HCl because the pH went from acidic to basic.

 

I cannot explain the foaming; it seems to me that the gas is water vapor since when you react an acid with a base you get water and a salt. HCl + NaOH----> H2O + NaCl, in your case. The foam was formed as a result of the reaction occurring.

 

Sorry I can't be more help..Chemistry was never my favorite :/